Mini Split Sizing Calculator
BTU size for a ductless mini split from room size and conditions.
Enter your values
ⓘ Live results
- Recommended unit
- 9,000 BTU/hr (0.8 ton)
- Calculated load
- 8,000 BTU/hr
- Load per sq ft
- 20 BTU/hr-ft2
Working
- 1400 ft2 x 20 x 1 x 1 x 1 = 8,000 BTU/hr
Quick answer
Start with about 20 BTU per square foot, then adjust for ceiling height, insulation quality, sun exposure, occupants and kitchen heat.
BTU = area x 20 x height factor x insulation factor + adders
How to use the Mini Split Sizing Calculator
- 1Enter the room area and true ceiling height.
- 2Adjust for insulation and sun - a west-facing glass wall changes the answer a lot.
- 3Round up to the next standard head size, but avoid oversizing by more than one step.
Worked example
Using the values the calculator loads with:
Inputs
- Room area400 sq ft
- Ceiling height8 ft
- InsulationAverage
- Sun exposureAverage
- Regular occupants2
- Kitchen in this spaceNo
Results
- Recommended unit9,000 BTU/hr (0.8 ton)
- Calculated load8,000 BTU/hr
- Load per sq ft20 BTU/hr-ft2
- 400 ft2 x 20 x 1 x 1 x 1 = 8,000 BTU/hr
Frequently asked questions
Is bigger always better?
No. An oversized mini split short-cycles, never runs long enough to dehumidify, and leaves the room clammy. Sizing close to the load is what makes inverter units efficient.
Does this replace a Manual J?
It is a fast planning estimate. For a whole-house system or a tight budget, a proper Manual J load calculation is still the gold standard.
About this calculator
- Built and reviewed by James Whitfield · How we build and test calculators
- Report an error
Results are estimates for general information. For medical, legal, structural or financial decisions, confirm with a qualified professional.